On September 21, 2012 Johnson set the Orioles' all-time single season save record at 46, passing Randy Myers. Johnson recorded his 50th save of the season on September 30 after a win over the Boston Red Sox. With the win, Baltimore clinched a post-season berth and Johnson became the 10th pitcher in MLB history to record 50 saves or more. He finished the season with 51 saves. He won the AL Rolaids Relief Man Award.
Johnson had a mediocre postseason debut through four games in the 2012 American League Division Series against the New York Yankees. Johnson struggled in game one of the series at Camden Yards, entering in the 9th inning of a 2–2 game and surrendered five runs (four earned) in only ⅓ of an inning. The Yankees won, 7–2. He gained redemption in game two, pitching a perfect 9th inning to preserve a 3–2 advantage, striking out Alex Rodriguez on a 3–2 count to end the game. Johnson pitched again in game three in the Bronx and surrendered a game-tying home run to Raúl Ibañez with one out in the 9th inning. (Ibañez would also win the game on a homer in the 12th. off of Brian Matusz) Johnson earned a successful save in game four, working a scoreless 13th inning.
Johnson throws four pitches, leading with a hard sinker averaging 95 mph. His main off-speed pitch to right-handed hitters is a curveball averaging about 80 mph. Against lefties, Johnson adds an upper-80s changeup. Lastly, he throws an occasional four-seam fastball in the mid 90s.